Conventionally, a coated tool having a hard coating layer composed of the following lower layer (a) and upper layer (b) formed by deposition on the surface of a tungsten carbide-based cemented carbide substrate (hereinafter referred to as a carbide substrate) or a TiCN-based cermet substrate (hereinafter referred to as a cermet substrate; in addition, an carbide substrate and a cermet substrate will be collectively referred to as a cutting tool body) has been widely known (for example, Patent Document 1).
(a) The lower layer: a Ti compound layer composed of one or more layers of a TiC layer, a TiN layer, a TiCN layer, a TiCO layer, and a TiCNO layer having an average overall layer thickness of 3 μm to 20 μm.
(b) The upper layer: an aluminum oxide (hereinafter expressed as Al2O3) layer having an average layer thickness of 1 μm to 15 μm and an α-type crystalline structure of a state formed by chemical vapor deposition.
This coated tool is known to exhibit excellent wear resistance in a cutting process of steel, cast iron, and the like.
In addition, a coated tool in which the grain width of a TiCN layer composing a lower layer of a hard coating layer is set to 0.01 μm to 0.5 μm in order to improve the fracture resistance, impact resistance, wear resistance, and the like of the coated tool is known (for example, Patent Literature 2).